Characterization of higher harmonic modes in Fabry\u2013P\xe9rot microcavity organic light emitting diodes

Ekraj Dahal,David Allemeier,Matthew S. White,Benjamin Isenhart,Karen Cianciulli

doi:10.1038/s41598-021-87697-8

Ekraj Dahal, David Allemeier + Show 3 more

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https://doi.org/10.1038/s41598-021-87697-8

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Abstract

Encasing an OLED between two planar metallic electrodes creates a Fabry–Pérot microcavity, resulting in significant narrowing of the emission bandwidth. The emission from such microcavity OLEDs depends on the overlap of the resonant cavity modes and the comparatively broadband electroluminescence spectrum of the organic molecular emitter. Varying the thickness of the microcavity changes the mode structure, resulting in a controlled change in the peak emission wavelength. Employing a silicon wafer substrate with high thermal conductivity to dissipate excess heat in thicker cavities allows cavity thicknesses from 100 to 350 nm to be driven at high current densities. Three resonant modes, the fundamental and first two higher harmonics, are characterized, resulting in tunable emission peaks throughout the visible range with increasingly narrow bandwidth in the higher modes. Angle resolved electroluminescence spectroscopy reveals the outcoupling of the TE and TM waveguide modes which blue-shift with respect to the normal emission at higher angles. Simultaneous stimulation of two resonant modes can produce dual peaks in the violet and red, resulting in purple emission. These microcavity-based OLEDs employ a single green molecular emitter and can be tuned to span the entire color gamut, including both the monochromatic visible range and the purple line.

Highlights

Encasing an Organic light-emitting diodes (OLEDs) between two planar metallic electrodes creates a Fabry–Pérot microcavity, resulting in significant narrowing of the emission bandwidth
The microcavity OLED employs two reflective surfaces, either two metallic electrodes or one dielectric mirror, which limits the emission to narrow-band resonant cavity modes due to exciton-photon coupling[3,4,5,6,7,8]
The mirrors act as cathode and anode, between which the electron transport layer (ETL), the emissive layer (EML), and the hole transport layer (HTL) of the OLED occupy the volume of the etalon

Summary

Introduction

Encasing an OLED between two planar metallic electrodes creates a Fabry–Pérot microcavity, resulting in significant narrowing of the emission bandwidth The emission from such microcavity OLEDs depends on the overlap of the resonant cavity modes and the comparatively broadband electroluminescence spectrum of the organic molecular emitter. Simultaneous stimulation of two resonant modes can produce dual peaks in the violet and red, resulting in purple emission These microcavity-based OLEDs employ a single green molecular emitter and can be tuned to span the entire color gamut, including both the monochromatic visible range and the purple line. We employ a Si-wafer substrate to act as a built-in heat sink to enable high-power operation of microcavity OLEDs with 100–350 nm thickness This range allows for the EML semiconductor Tris(8-hydroxyquinolinato)aluminum ( Alq3 ) to directly pump the fundamental and first two higher harmonics, revealing a larger picture of the cavity mode structure

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